With more and more individuals connected to the Internet and having electronic mail (email) accounts, it has become feasible for advertisers and other groups or individuals to disseminate advertisements and promotions to a large audience. Many such advertisements and promotions are sent as unwanted email messages (spam) to large numbers of email users.
Many email systems include filters for reducing the amount of unwanted email messages (spam). As spam filtering techniques are learned by spammers, they frequently find ways to develop email messages that can pass through spam filters. One attribute of an email message that is difficult to conceal or alter is a sender identity (e.g., an IP address or domain from which the email address was sent). Accordingly, many existing spam filters are designed to filter email based on data that indicates who sent the message or where the message was sent from, for example, by analyzing an IP address from which the message was received or by analyzing sender information that is part of a message header. Other existing spam filters are configured to filter email messages based on contents of a received message. In some existing implementations, an email filter may be designed to filter email by examining both sender information and message contents, marking a message as spam if either the sender information or the message contents indicates that the message is likely spam. While this type of spam filter may accurately identify many email messages as spam, it also tends to falsely identify email messages with innocuous content as spam. For example, a particular IP address may be identified as being the sender of a large quantity of spam messages. A non-spam message sent from the same IP address may be determined by a spam filter as being spam based solely on the sender information, when, in fact, the message contents are perfectly innocuous. This leads to user frustration and dissatisfaction with existing spam filters.
Accordingly, a need exists for a spam filter that considers both a sender identity and other features of the message (e.g., the message content) when filtering email so that a message is not identified as spam based on a sender identity unless the message contents are also at least somewhat indicative of spam.